There are 2 main ways to get citations into MyEndnoteWeb: one is to is to hand-enter them yourself; the other is to import them from one of the research databases.
There is a Firefox toolbar you can install to assist in importing citations as well.
Importing from databases
Many library subscription databases available through the web can export citations either directly into EndnoteWeb or indirectly, by exporting a citation file that you then upload into Endnote web.
Exporting Directly from a Database into MyEndnoteWeb
Exporting to a File and Uploading to EndnoteWeb
Some database products don't have a direct export-to-EndnoteWeb option. For them, you will need to Export a list of your citations and Import them into Endnote web. If you use the Mozilla Toolbar for Endnote Web, the process skips a few steps.
Summon is currently one of those databases.